We propose to measure respiratory and cardia function at extreme altitudes during the 1981 American Medical Research Expedition to Everest. Although some physiological data are available up to altitudes of about 7440 m (24,400 feet), very few measurements have been made above this. However, the conditions are of great physiological and medical interest because they represent the limit of man's ability to survive breathing ambient air. We shall collect data on cardiopulmonary function on climbers above 7440 m (24,400 feet) and expect to make the first measurements on man on the summit of Mt. Everest at 8848 m (20,028 feet). Measurements will include alveolar gas concentration, barometric pressure, total ventilation, oxygen uptake, heart rate, rhythm, and ECG waveform. The physiologic variables will be recorded on miniature magnetic tape recorders worn by the climpers. Scientist-climbers working in a laboratory tent erected on the South Col at 7990 m (26,200 feet) will assist in these measurements. Additional data will be obtained in a Laboratory Camp at an altitude of approximately 6100 m (20,00 feet). A small, warm, rigid hut will house the scientific equipment. Arterial oxygen saturation will be measured by ear oximetry during exercise with the subjects breathing ambient air and low O2 concentration. Additional measurements will be made during sleep. Oxygen dissociation curves will be measured, and frozen blood samples will be brought back for measurements of 2,3 diphosphoglycerate. Chest radiographs will be taken for evidence of pulmonary hypertension and edema. It is expected that the resulting information will throw light on the physiologic responses of the body to extreme hypoxia and ultimately may lead to improvement in our understanding and management of patients with advanced cardiopulmonary disease.